The Federal Aviation Administration has not done enough to tighten safety rules for the growing volume of airplane maintenance that airlines are outsourcing to contractors, the Department of Transportation's internal watchdog told Congress yesterday.

DOT Inspector General Calvin Scovel said the current FAA program that asks airlines to voluntarily report where they outsource key maintenance doesn't work because not all airlines comply. The FAA's voluntary process for airlines to report their top 10 "critical maintenance" providers has produced reports from only seven of nine carriers.

He said the FAA cannot adequately oversee the quality of maintenance because it has no way of knowing where all the work is done.

Critics and defenders of the FAA's maintenance oversight testified before the House aviation subcommittee.

Nicholas Sabatini, the FAA's associate administrator for aviation safety, defended the agency's oversight of an industry that he said has become "incredibly complex." Terrorism and high fuel prices forced airlines to slash costs to survive, pushing them to seek a wider variety of contractors to maintain their fleets.

He called Scovel's proposed oversight reforms unrealistic.

The last U.S. plane crash blamed on maintenance occurred in January 2003 in Charlotte, N.C. An unlicensed maintenance contractor improperly adjusted a flight control on an Air Midwest aircraft being flown for US Airways Express. The plane crashed on takeoff the next day, killing all 21 aboard.